Visiting Vet: Human ointments and creams are bad news when ingested by pets

Like many baby boomers who spent their youth eschewing sunblock while basking on the beach, I now have some pesty spots on my face called actinic keratosis. Also known as solar keratosis, these rough, scaley patches are often considered precancerous, so my dermatologist repeatedly froze the areas with liquid nitrogen. But the spots kept coming back, so we moved on to a topical form of chemotherapy called fluorouracil, also known as Carac, Fluoroplax, Efudex, 5-fluorouracil, or just 5 F-U. I would apply a dab to each spot, then blot off the excess with a tissue, that I then tossed in the bathroom trash. What I didn’t think about was the fact that our bathroom trash has no lid and is full of dog-tempting items like paper products and dental floss.

We all know medications that come as pills and capsules and are dispensed in vials with child-proof caps can be problematic if Flyer, the Foxhound, eats them, but what about when he chews up a tube of antibiotic ointment? Or eats a tissue tossed in the trash after wiping the 5-FU? Let’s talk topical toxicity.

A topical medication is one that is applied to the skin. It may be intended to work locally, like antibiotic ointment on a cut, or to absorb into the blood, like a nicotine patch for quitting smoking. But it is never intended to be eaten, and although most topicals are relatively safe even if ingested, some are not, and a few are truly deadly.

Over-the-counter topicals like antibiotic or steroid ointments, and zinc-containing products such as diaper rash ointment and some sunscreens typically cause only mild self-limiting illness when ingested, but if Flyer eats a tube of something, be sure you know what was in it, and check with your veterinarian. Zinc oxide is a strong gastric irritant, so if Fly downs the Desitin, he may end up with a bad bout of vomiting. Treatment is simple supportive care except in the rare situation where an animal ingests enough to cause actual zinc poisoning, which causes severe anemia and usually requires blood transfusions.

Most veterinary cases of true zinc poisoning are the result of dogs swallowing pennies, which since 1983 have been made of zinc with a thin copper coating, but there is one reported case in which a person was applying a thick coating of diaper cream to a rectal mass on a dog every day. The dog then proceeded to lick it off, ultimately eating about three-quarters of a pound of Desitin over a four-day period, resulting in severe zinc poisoning. The dog survived but only after aggressive treatment.

Then we have “natural” products, like tea tree oil. It’s natural so it must be safe, right? Wrong. Extracted from leaves of the Australian Melaleuca alternafolia tree, this stuff is relatively safe when diluted, but many people buy it as pure oil. Put that high test product on Fly’s skin, and it will rapidly absorb into his blood stream. Even worse if he eats it. Less than two teaspoons can be toxic, whether ingested or applied to the skin, causing weakness, central nervous system depression, incoordination, tremors, hypothermia, even liver damage. Treatment is supportive care, and removing as much of the product as possible by washing Fly with something like Dawn dishwashing soap which is good at removing oily substances.

Oil of wintergreen is another of those things that sounds harmless. It’s in all kinds of ointments, liniment, and sports rubs. BenGay, Heet, Icyhot. Or you can buy pure oil in homey-looking little bottles that make you feel all organic. But despite its plant origins, and the fact that you may think of it as simply a flavor of gum or kind of tea, oil of wintergreen is methyl salicylate, a relative of acetylsalicylic acid, i.e., aspirin. You can find salicylates in many medicated face washes and acne control products from Noxema to Clearasil.

Salicylate overdose can lead to vomiting, gastrointestinal bleeding, elevated body temperature, weakness, depression, and incoordination. In very severe cases you can see stomach perforation, anemia, clotting problems, liver or kidney failure, and coma. There is no antidote, so treatment involves supportive care. Dogs can metabolize and excrete salicylates pretty rapidly, but cats cannot, putting them at much greater risk of salicylate poisoning.

People are not immune either. The death of one teenage athlete was attributed to overuse of a topical oil of wintergreen product. One teaspoon of pure oil of wintergreen is equivalent to about 20 adult-strength aspirin tablets and drinking it has caused quite a number of fatalities in small children. I doubt any of the people involved in these tragic cases had any idea the product could be lethal.

Which brings us back to 5-FU. Even tiny amounts can be toxic to pets. For cats, any exposure at all is dangerous. If you apply some to your face, forget to wash up, then go pat Purrbaby, who then grooms herself, ingesting a dab of 5-FU… It could be fatal. In dogs, it may take a little more, but it is still extraordinarily toxic. If Fly chews that tube, clinical symptoms develop within five hours including persistent vomiting, sloughing of the gastrointestinal tract, multiple organ failure, and severe seizures that do not respond to treatment. Seventy-five percent of affected dogs die within one week. So when I came home one day to find our dog, Flower, had happily tossed the bathroom trash in search of tasty tidbits, I was really worried. From then on I made sure tissues used to dab 5-FU were discarded in a pet-proof bin.

Don’t assume that because you can buy something over the counter, or because it comes in a tube, or because it’s “natural,” that it’s not dangerous. Keep these products stored securely. Remember, dogs and cats will lick off goop you apply topically. Check with your veterinarian before intentionally putting anything on your pet, and also if Fly gets into the ointment or anything else he shouldn’t.